Since three months ago, the number of students making notes while listening in class ________ 90％．A.has increased byB.was increased toC.have increased forD.had increased by
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A解析since three months ago是现在完成时的时间状语，所以句子的时态要用现在完成时。increase by 意思是“增长了多少”，而increase to为“增长到(一个具体的数字)”。the number of students意思是“学生的数目”，谓语动词应该用单数形式。